We solved the sedimentation equilibrium problem using a generalized flash algorithm, in which we specify the temperature, global particle number density, total volume, and height of the system. The minimization of a thermodynamic potential that takes into account the effect of the gravitational field yields the equilibrium distribution profiles. We used a hard-sphere-mixture equation of state as the thermodynamic model. The results showed to be in good agreement with both experimental data for identical spheres and Monte Carlo simulations for binary systems. We also present a methodology suitable to calculate sedimentation equilibrium in more complex systems, containing more than one solid, each of them characterized by its own size distribution.